Also because you have a WRT54GS 1.1 it should have 8MB of flash, it should tell you that on the main overview page.
So any firmware that is smaller than 8MB from here should work
If you want IPv6 look here, only the firmwares that have MIPSR1 in the file name and are smaller than 8MB work.
Look in the builds.png to see what options are in each build.

Thanks for the head start. I'm still a bit confused especially because what I was reading before was saying that K26 builds won't work on these...is that true?

It does look like my router is of the 8/32MB variety, so if it was simply a memory issue, then I guess I should be able to handle it?

Also from my recollection when I updated before I used .bin files.. (I think), but the MIPSR1 are all TRX files... are these interchangeable?

Looking at that build.png it looks like it is saying there is a MAX version in K24 that supports both IPV6, VLAN, and OpenVPN (2nd column)...but I can't find that file anywhere... Am I reading this chart right?

Ideally, if someone could just point me to a version that will run on my 8MB WRT54GS that supports OpenVPN and preferable VLAN and IPV6 I would really appreciate it!

I have a K26 build running on my WRT54GL, so the K26 builds mentioned should work.

TRX and BIN files are basically the same when updating from tomato, only keep the size and MIPSR1 in mind.
Keep the firmware you chose under 7.5MB because the bootloader and settings also go inside the 8MB.

Not all versions in the build chart are actually made for every router so its possible that some are not available.

I went ahead (before your reply) and risked using "tomato-K26-1.28.RT-MIPSR1-114-Max.trx"

Everything came up fine with my same config as before, but then after choosing the "tomatoanon" settings it requests at first launch the router reset back to what seemed to be a default config. I did a through erase of NVRAM and set things back to basics and my basic internet seems to be functioning fine right now.

I need to play around with the open VPN client and also see if I can get the VLAN functionality doing what I want.

I don't have full IPV6 from my ISP yet...I think they are going to make me buy my own modem if I want to support it, but I need to talk with them about it. I might set up a 4to6 tunnel when I have some time.